Semiconductor device

ABSTRACT

A semiconductor device includes a first circuit, a second circuit, a first power supply line, a second power supply line coupled to the first circuit, a third power supply line, a fourth power supply line coupled to the second circuit, a first switch circuit including a first switch transistor and a well tap, the first switch transistor including one source or drain end coupled to the first power supply line and another source or drain end coupled to the second power supply line, the well tap being electrically coupled to the second power supply line, and a second switch circuit including a second switch transistor including one source or drain end coupled to the third power supply line and another source or drain end coupled to the fourth power supply line, the second switch circuit including no well tap electrically coupled to the fourth power supply line.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is based upon and claims the benefit of priorityfrom the prior Japanese Patent Application No. 2017-089407 filed on Apr.28, 2017, with the Japanese Patent Office, the entire contents of whichare incorporated herein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The disclosures herein relate to a semiconductor device.

2. Description of the Related Art

As known in the art of semiconductor devices, technologies for reducingleak current in a target circuit cut the power to the target circuitwhen it is not operating. In such technologies, a power switch circuitis provided between a power supply line and a target circuit in asemiconductor device. Power voltage is applied to the target circuit viathe power switch circuit when the target circuit is to operate, and iscut by the power switch circuit when the target circuit is not tooperate.

Specific technologies known in the art include semiconductor devices andthe like which include a switch cell to supply or cut the power to anarea for which power supply is stoppable (see Patent Document 1, forexample).

However, no known technologies provide the configuration of power switchcircuits usable for respective, different types of target circuits.

[Patent Document 1] Japanese Patent Application Publication No.2013-110419 [Patent Document 2] Japanese Patent Application PublicationNo. 2016-001652 [Patent Document 3] Japanese Patent ApplicationPublication No. 2011-159810 [Patent Document 4] Japanese PatentApplication Publication No. 2011-243794 [Patent Document 5] JapanesePatent Application Publication No. 2012-234593 SUMMARY OF THE INVENTION

It is a general object of the present invention to provide asemiconductor device that substantially obviates one or more problemscaused by the limitations and disadvantages of the related art.

According to an embodiment, a semiconductor device includes a firstcircuit formed in a semiconductor substrate, a second circuit formed inthe semiconductor substrate, a first power supply line, a second powersupply line coupled to the first circuit, a first ground line, a thirdpower supply line, a fourth power supply line coupled to the secondcircuit, a second ground line, a first switch circuit including a firstswitch transistor and a well tap of the semiconductor substrate, thefirst switch transistor including a first source and a first drain, oneof the first source and the first drain being coupled to the first powersupply line, another of the first source and the first drain beingcoupled to the second power supply line, and the well tap beingelectrically coupled to the second power supply line, and a secondswitch circuit including a second switch transistor, the second switchtransistor including a second source and a second drain, one of thesecond source and the second drain being coupled to the third powersupply line, another of the second source and the second drain beingcoupled to the fourth power supply line, the second switch circuitincluding no well tap of the semiconductor substrate electricallycoupled to the fourth power supply line.

According to at least one embodiment, power switch circuits usable forrespective, different types of target circuits are provided.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and further features of the present invention will beapparent from the following detailed description when read inconjunction with the accompanying drawings, in which:

FIG. 1 is a drawing illustrating power gating;

FIGS. 2A and 2B are drawings illustrating power switch circuitsaccording to a first embodiment;

FIGS. 3A through 3C are drawings illustrating an example of asemiconductor device of the first embodiment;

FIG. 4 is a drawing schematically illustrating a power switch circuitaccording to the first embodiment;

FIG. 5 is a drawing illustrating coupling between the well-tap areas andpower supply of a first power switch circuit of the first embodiment;

FIG. 6 is a drawing illustrating the layout of the first power switchcircuit according to the first embodiment;

FIG. 7 is a drawing illustrating a cross-section of the first powerswitch circuit according to the first embodiment;

FIG. 8 is a drawing illustrating coupling between a target circuit andthe first power switch circuit of the first embodiment;

FIG. 9 is a drawing illustrating a second power switch circuit accordingto the first embodiment;

FIG. 10 is a drawing illustrating the layout of the second power switchcircuit according to the first embodiment;

FIG. 11 is a drawing illustrating a cross-section of the second powerswitch circuit according to the first embodiment;

FIG. 12 is a drawing illustrating another layout of the second powerswitch circuit according to the first embodiment;

FIG. 13 is a drawing illustrating the power supply lines of thesemiconductor device according to the first embodiment;

FIG. 14 is a drawing schematically illustrating a power switch circuitaccording to a second embodiment;

FIG. 15 is a drawing illustrating coupling between the well-tap areasand power supply of a first power switch circuit of the secondembodiment;

FIG. 16 is a drawing illustrating a second power switch circuitaccording to the second embodiment;

FIG. 17 is a drawing illustrating the layout of the first power switchcircuit according to a third embodiment;

FIG. 18 is a drawing schematically illustrating a FinFET; and

FIG. 19 is a drawing schematically illustrating a nanowire transistor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

In the following, power gating will be first described with reference todrawings, ahead of the description of a first embodiment.

FIG. 1 is a drawing illustrating power gating; For power gating, a MOS(metal-oxide semiconductor) switch 3 is placed between a power supplyline VDD and a target circuit 2 in a semiconductor device 1. Supply ofpower voltage from the power supply line VDD to the target circuit 2 iscontrolled. The MOS switch 3 is an example of a power switch circuit tocontrol whether to supply or cut the power to the target circuit 2.

In the semiconductor device 1, the MOS switch 3 is placed in the offstate by a PMU (power management unit) 4 to cut the power to the targetcircuit 2. In the semiconductor device 1, the MOS switch 3 is placed inthe on state by the PMU 4 when the target circuit 2 is to operate. Asthe MOS switch 3 is placed in the on state, a power supply line VirtualVDD (which will hereinafter be referred to as VVDD) for supplying powerto the target circuit 2 is coupled to the power supply line VDD, therebysupplying power to the target circuit 2.

Power gating is a power reduction technology that controls whether tosupply or cut the power to the target circuit 2 to reduce the occurrenceof leak current in the target circuit 2.

A typical semiconductor device includes various types of circuitsimplemented as target circuits. Specifically, target circuits mayinclude logic circuits such as standard cells, RAM circuits such asSRAMs (static random access memories), analog macro circuits, and thelike. The analog macro circuits may include analog-to-digital conversioncircuit (ADC) for converting analog signals from an external device intodigital signals, a digital-to-analog conversion circuit (DAC) forconverting digital signals into analog circuits, and the like.

There may be a case in which the threshold voltage of a transistor iscontrolled by applying potential not only to the source and drain of thetransistor but also to the substrate. In the following, an area forapplying potential to the substrate (i.e., applying potential to a wellformed in the substrate) will be referred to as a well-tap area.

In some cases, a standard cell may not include a well-tap area. In thesecases, a well-tap area is disposed in addition to such a standard cellwhere the standard cell is placed. In the case of such a standard cellbeing a target circuit, a well-tap area is disposed inside a powerswitch circuit.

In contrast, analog macro circuits, memory circuits, and the like mayinclude a well-tap area disposed inside these circuits. When suchcircuits including a well-tap area are target circuits, the well-taparea inside a power switch circuit may not be used.

In consideration of the above, the following embodiments will utilize,in a semiconductor device, power switch circuits that are usable for atarget circuit including no area for applying potential to the substrateand usable for a target circuit including an area for applying potentialto the substrate, respectively.

More specifically, a power switch circuit including a well-tap area isused for a target circuit including no area for applying potential tothe substrate, thereby controlling whether to supply or cut power in thesemiconductor device. Further, a power switch circuit including nowell-tap area is used for a target circuit including an area forapplying potential to the substrate, thereby controlling whether tosupply or cut power in the semiconductor device.

As described above, the present embodiment utilizes power switchcircuits usable for respective, different types of target circuits. Awasted circuit area for wasted well-tap areas is thus eliminated in asemiconductor device, which serves to reduce the size of thesemiconductor device.

In the following, a power switch circuit of the present embodiment willbe described with reference to FIGS. 2A and 2B. FIGS. 2A and 2B aredrawings illustrating power switch circuits according to a firstembodiment. FIG. 2A is a drawing schematically illustrating a powerswitch circuit including a well-tap area. FIG. 2B is a drawingschematically illustrating a power switch circuit including no well-taparea.

A power switch circuit 200 illustrated in FIG. 2A includes a powerswitch section 21 and well-tap areas 22-1 and 22-2 adjoining the powerswitch section 21 on the respective sides thereof. A power switchcircuit 210 illustrated in FIG. 2B is a power switch section 31 byitself, without the well-tap areas 22-1 and 22-2. In the presentembodiment, the power switch section 21 and the power switch section 31include the same configuration.

Because of the noted structure, a width X2 of the power switch circuit210 in the X-axis direction is narrower than a width X1 of the powerswitch circuit 200 in the X-axis direction in the X-Y coordinate systemillustrated in FIG. 2. A width Y1 of the power switch circuit 200 and awidth Y2 of the power switch circuit 210 in the Y-axis direction areequal to each other.

As described above, the present embodiment makes selective use of thepower switch circuit 200 and the power switch circuit 210 depending onthe type of a target circuit, thereby reducing the implemented circuitarea compared to the case in which the power switch circuits 200 areused for all the target circuits.

In the following, the power switch circuit 200 may sometimes be referredto as a first power switch circuit, and the power switch circuit 210 maysometimes be referred to as a second power switch circuit. The detailsof the power switch circuit 200 and the power switch circuit 210 will bedescribed later.

In the following, a semiconductor device according to the presentembodiment will be described. FIGS. 3A through 3C are drawingsillustrating an example of a semiconductor device of the firstembodiment. FIG. 3A is a plan view of an area 41 in which a targetcircuit is placed in a semiconductor device 30. FIG. 3B is an enlargedview of an area enclosed in a dotted circle B in FIG. 3A. FIG. 3C is anenlarged view of an area enclosed in a dotted circle C in FIG. 3A.

The area 41 of the semiconductor device 30 of the present embodimentincludes an area 42 in which standard cells (logic circuits) 40 and thelike are disposed, and includes an area 43 in which the standard cells(logic circuits) 40 and the like are not disposed. Further, the area 41includes circuits 50, such as RAMs and analog circuits, including anarea for applying potential to the substrate.

In the following, the area 42 in which the standard cells (logiccircuits) 40 and the like are disposed will be referred to as a firstarea, and the area 43 in which the standard cells (logic circuits) 40and the like are not disposed will be referred to as a second area. Thesecond area 43 includes the power switch circuits 210 and othersdisposed therein. The first area 42 includes the power switch circuits200 disposed in a staggered arrangement, for example.

The area 41 includes power supply lines 206 and 207, which are coupledto the standard cells 40 and the like. The power supply lines 206 and207 extend in the X direction. As illustrated in FIG. 3A, the powersupply lines 206 and 207 may be terminated at the edges of the area 41(or the first area 42). Power supply lines 306 and 307, which will bedescribed later, may also be terminated at the edges of the area 41 (orthe second area 43). It may be noted that, although FIG. 3A illustratesonly one pair of power supply lines 206 and 207, a plurality of pairs ofpower supply lines 206 and 207 may be provided.

As illustrated in FIGS. 3B and 3C, the present embodiment may includedummy line patterns situated outside the area 41 (i.e., outside thefirst area 42 and the second area 43). In FIG. 3B, the dummy linepatterns 95 is disposed outside the first area 42. In FIG. 3C, the dummyline patterns 95 is disposed outside the second area 43.

The dummy line patterns 95 refer to line patterns that are not coupledto the transistors or lines of the circuits, for example. Provision ofthe dummy line patterns 95 serves to improve evenness of the productionprocess for forming lines.

The power supply lines 206 and 207 extending in the X direction in thepresent embodiment may be terminated before reaching the dummy linepatterns 95 as illustrated in FIG. 3B.

In the present embodiment, the power supply lines 306 and 307, which aredisposed in the second area 43 and will be described later, may also beterminated before reaching the dummy line patterns 95. The dummy linepatterns 95 may be arranged to surround the area 41.

When another circuit area is disposed alongside the area 41, dummy linepatterns may not be placed. In such a case, the power supply lines 206and 207 and the power supply lines 306 and 307 may be terminated beforereaching such an adjoining circuit area.

The example illustrated in FIGS. 3A through 3C depicts only some and notall of the standard cells 40 implemented in the first area 42. The firstarea 42 in actuality may include a larger number of standard cells 40implemented therein.

The second area 43 includes an area between the circuits 50, an areabetween one of the circuits 50 and an edge of the area 41, and the like.In the second area 43, the power switch circuits 210 are aligned in theY direction along one or more circuits 50.

As described above, the semiconductor device 30 of the presentembodiment include the first area 42 in which the power switch circuits200 usable for the standard cells 40 are disposed, and include thesecond area 43 in which the power switch circuit 210 usable for thecircuits 50 are disposed. This arrangement allows the size of the secondarea 43 to be reduced compared with the case in which the power switchcircuits 200 are used for all the standard cells 40 and the circuits 50,thereby serving to reduce the size of the semiconductor device 30.

Some of the circuits 50 include an edge situated alongside the firstarea 42 and an edge situated alongside the second area 43. Terminals 51for coupling to the standard cells 40 in the first area 42 are disposedalong the edge situated alongside the first area 42. The terminals 51may be used by the circuits 50 to receive signals from the standardcells 40 and to transmit signals from the circuits 50 to the standardcells 40. The terminals 51 are preferably arranged at the edge alongsidethe first area 42 for the purpose of reducing signal attenuation and thelike. In contrast, the second area 43 is preferably situated alongsidethe edge of the circuit 50 where no terminals 51 are disposed, from theviewpoint of an efficient circuit arrangement.

The terminals 51 illustrated in FIG. 3A are examples only. The number ofterminals 51 disposed in one of the circuits 50 may be two, or may befour or more.

In the following, a description will be given of the power switchcircuit 200 and the power switch circuit 210 according to the presentembodiment. FIG. 4 is a drawing schematically illustrating a powerswitch circuit according to the first embodiment.

The power switch circuit 200 and the power switch circuit 210 of thepresent embodiment are each a power switch circuit with one input andone output. The power switch circuit 200 and the power switch circuit210 of the present embodiment have the same circuit configuration. FIG.4 illustrates the power switch circuit 200 as a representative example.

The power switch circuit 200 of the present embodiment includes atransistor 25, a buffer 26, a T_(IN) terminal, a T_(OUT) terminal, aT_(VDD) terminal, a T_(VVDD) terminal, and a T_(VSS) terminal.

The transistor 25 is a switch transistor. The buffer 26, which includesan inverter 27 and an inverter 28, drives the transistor 25.

The T_(IN) terminal, which is coupled to the input of the buffer 26,receives a control signal for controlling whether to supply or cut thepower to a target circuit. The T_(OUT) terminal, which is coupled to theoutput of the buffer 26, transmits the control signal applied to theT_(IN) terminal. The T_(VDD) terminal, which is coupled to one end ofthe transistor 25, is coupled to the power supply. The T_(VVDD)terminal, which is coupled to the other end of the transistor 25, iscoupled to the target circuit.

The transistor 25 is a PMOS transistor having the on and off stateswhich are controlled in response to the signal supplied from theinverter 27 of the buffer 26. The inverter 27 is coupled to the T_(VSS)terminal and to the T_(VDD) terminal. The T_(VSS) terminal is a groundconnection terminal that is coupled to the ground.

In the present embodiment, the on state of the transistor 25 causes theT_(VDD) terminal and the T_(VVDD) terminal to be coupled to each other,so that the power supply potential to which the T_(VDD) terminal isconnected is supplied to the T_(VVDD) terminal. The power supplypotential is thus supplied from the T_(VVDD) terminal to the targetcircuit.

The off state of the transistor 25 causes the power to the T_(VVDD)terminal to be cut.

In the following, the power switch circuit 200 of the present embodimentwill be described with reference to FIG. 5 through FIG. 7. FIG. 5 is adrawing illustrating coupling between the well-tap areas and powersupply of a first power switch circuit of the first embodiment.

The power switch circuit 200 of the present embodiment includes N-typewells 202, 203, and 204 formed in a P-type substrate 201. The powerswitch circuit 200 of the present embodiment further includes a powersupply line 205 corresponding to the power supply line VDD, a powersupply line 206 corresponding to the power supply line VVDD, and powersupply lines 207 corresponding to the power supply line VSS.

The power supply line 205, which is formed over the P-type substrate201, is electrically coupled to the N-type well 202. The power supplyline 206 is formed over the P-type substrate 201 to span across theN-type wells 202, 203, and 204 in a plan view. The power supply line 206is electrically coupled to the N-type wells 203 and 204.

At least part of the N-type well 203 is included in the well-tap area22-1, and at least part of the N-type well 204 is included in thewell-tap area 22-2.

The transistor 25 is formed to provide coupling between the power supplyline 205 and the power supply line 206 in the N-type well 202. The gateelectrode of the transistor 25 is coupled to the output of the firstinverter 27 of the buffer 26. The inverter 27 and the inverter 28 arecoupled between the power supply line 205 and the power supply lines207.

A contact 217 is formed above the N-type well 202 and the N-type well202 is coupled to the power supply line 205 via the contact 217. Acontact 213 and a contact 214 are formed above the N-type wells 203 and204 respectively. The N-type wells 203 and 204 are coupled to the powersupply line 206 corresponding to the power supply line VVDD via thecontact 203 and 204 respectively.

In the present embodiment, the potential of the power supply line VVDDis applied to the substrate of the target circuit through the N-typewells 203 and 204.

It may be noted that a standard cell is formed to include transistorsdisposed between the power supply line 206 and the power supply line 207extending in the same direction. When target circuits are standardcells, thus, the target circuits are aligned one next to another in thedirection in which the power supply lines 206 and 207 extend. The powerswitch circuit 200 of the present embodiment includes the well-tap areas22-1 and 22-2 aligned on the respective ends of the power switch circuit200 in the direction in which power supply lines 206 and 207 extend,thereby being capable of efficiently supplying potential to standardcells.

It may be noted that the standard cells 40 may not only be formedbetween the power supply line 206 and the power supply line 207 adjacentto each other, but also be formed for coupling to the power supply line206 and the power supply line 207 that are not adjacent to each other.

In the following, the direction in which the power supply lines 206 and207 extend is referred to as the X-axis direction (or the firstdirection), and the direction perpendicular to the X-axis direction isreferred to as the Y-axis direction (or the second direction).

Although the present embodiment is directed to the configuration inwhich the well-tap areas 22-1 and 22-2 are formed on the respectivesides of the power switch section 21, this is not a limiting example.The power switch circuit 200 may include only one of the well-tap areas22-1 and 22-2 formed therein when a target circuit needing potential tobe applied thereto is situated only on one side of the power switchsection 21.

In the following, the power switch circuit 200 of the present embodimentwill be described with reference to FIG. 6 and FIG. 7.

FIG. 6 is a drawing illustrating the layout of the first power switchcircuit according to the first embodiment. FIG. 7 is a drawingillustrating a cross-section of the first power switch circuit accordingto the first embodiment. FIG. 7 illustrates the cross section takenalong the X-X′ line in FIG. 6.

The power switch circuit 200 of the present embodiment includes theP-type substrate 201, the N-type wells 202 through 204, STIs (shallowtrench isolations) 281 through 283, the power supply lines 205 through207, gate electrodes 208, P-type impurity regions 221 through 226,N-type impurity regions 231 through 234, and contacts 212 through 218.

The power switch circuit 200 of the present embodiment includes theN-type wells 202 through 204 formed in the P-type substrate 201. TheP-type impurity regions 221 and 222 and the N-type impurity region 231are formed in the N-type well 202. The N-type impurity region 233 isformed in N-type well 203. The N-type impurity region 234 is formed inthe N-type well 204.

In the present embodiment, the N-type impurity regions 232 and theP-type impurity regions 223 through 226 are formed in the P-typesubstrate 201.

The P-type impurity regions 221, which have a higher dopingconcentration than the P-type substrate 201, form the source and drainregions of the transistor 25. The transistor 25 includes the gateelectrodes 208, gate insulating films 252, and sidewalls 253 and 254. Inthe present embodiment, the gate electrodes 208 are electrically coupledto the output of the inverter 27. In the present embodiment, a pluralityof transistors 25 may be coupled in parallel to each other.

The transistors of the inverters of the buffer 26 include source anddrain regions as a part of the P-type impurity regions 222 and theN-type impurity regions 232. The P-type impurity regions 222 have ahigher doping concentration than the P-type substrate 201. Thetransistors of the inverters constituting the buffer 26 include gateelectrodes 271, gate insulating films 272, and sidewalls 273 and 274.

The power switch circuit 200 of the present embodiment includes the STIs281 through 283 formed in the P-type substrate 201 between the N-typewells and between the transistors. Further, a first interlayerinsulating film 261 is formed over the P-type substrate 201.

In the example illustrated in FIG. 7, interconnections such as the powersupply lines 205 through 207 are formed inside a second interlayerinsulating film that is formed over the first interlayer insulating film261. The second interlayer insulating film may be made of a lowdielectric constant material such as a porous film or an SiOC (siliconoxycarbide) film.

In the present embodiment, the N-type well 202 and the N-type well 203are arranged at a distance of L1 from each other in the X-axisdirection. Further, the N-type well 202 and the N-type well 204 arearranged at a distance of L2 from each other in the X-axis direction.

In the present embodiment, the distance L1 and distance L2 are such alength as to reduce an effect of a difference between the potential ofthe power supply line VDD applied to the N-type well 202 and thepotential of the power supply line VVDD applied to the N-type well 203and the N-type well 204.

Some of the P-type impurity regions 221 are coupled to the power supplyline 205 through the contacts 212 formed through the first interlayerinsulating film 261, and the others are coupled to the power supply line206 through the contacts 216 formed through the first interlayerinsulating film 261.

One of the P-type impurity regions 222 is coupled to the power supplyline 205 through the contact 218 formed through the first interlayerinsulating film 261.

The P-type impurity regions 221 and the P-type impurity regions 222 areisolated from each other by the STI 282. The P-type impurity regions 221and the N-type impurity region 231 are isolated from each other by theSTI 283.

The N-type impurity region 231 is coupled to the power supply line 205through the contact 217 formed through the first interlayer insulatingfilm 261.

The N-type impurity region 233 is coupled to the power supply line 206through the contact 213 formed through the first interlayer insulatingfilm 261, so that the power supply line 206 is electrically coupled tothe N-type well 203, which is connected to the N-type well of a targetcircuit situated next to the well-tap area 22-1.

The N-type impurity region 234 is coupled to the power supply line 206through the contact 214 formed through the first interlayer insulatingfilm 261, so that the power supply line 206 is electrically coupled tothe N-type well 204, which is connected to the N-type well of a targetcircuit situated next to the well-tap area 22-2.

The P-type impurity region 223 and the P-type impurity region 224 arecoupled to the power supply lines 207, respectively, through thecontacts 215 formed through the first interlayer insulating film 261.The P-type impurity region 223 and the P-type impurity region 224 allowsthe power supply lines 207 to be connected to the P-type substrate or tothe P-type well of the target circuit situated next to the well-tap area22-1, thereby applying the potential of the power supply lines 207 tothe target circuit.

The P-type impurity region 225 and the P-type impurity region 226 arecoupled to the power supply lines 207, respectively, through thecontacts 215 formed through the first interlayer insulating film 261.The P-type impurity region 225 and the P-type impurity region 226 allowsthe power supply lines 207 to be connected to the P-type substrate or tothe P-type well of the target circuit situated next to the well-tap area22-2, thereby applying the potential of the power supply lines 207 tothe target circuit.

As described above, the power switch circuit 200 of the presentembodiment includes the N-type impurity regions 233 and 234 of therespective well-tap areas 22-1 and 22-2 connected to the power supplyline VVDD, and also includes the P-type impurity regions 221 of thepower switch section 21 connected to the power supply line VDD.

Moreover, the N-type well 202 of the power switch section 21 and theN-type wells 203 and 204 of the respective well-tap areas 22-1 and 22-2are arranged at a distance of L1 or L2 from each other in the presentembodiment.

The contacts 212 through 218 of the present embodiment include a gluefilm which includes titanium nitride, and a tungsten film, for example.The power supply lines 205 through 207 include copper and a barriermetal film which includes tantalum or tantalum nitride, for example. Thefirst interlayer insulating film 261 may include a silicon dioxide film,for example. The STIs 281 through 283 may include a silicon dioxidefilm, for example.

In the present embodiment, the gate electrodes 208 and 271 may includepolysilicon or metal such as titanium nitride. The gate insulating films252 and 272 may include a silicon dioxide film or a film which includesone or more materials of an oxide of hafnium, zirconium, lanthanum,yttrium, aluminum, titanium, and tantalum.

The layout illustrated in FIG. 6 is the layout of planar transistors,which is not a limiting example. The power switch circuit 200 mayinclude fin transistors (i.e., FinFETs) or nanowire transistors arrangedtherein, for example. In such a case, gate electrodes extending in theY-axis direction may extend, in a plan view, across the fins of a FinFETstructure or the nanowires of a nanowire transistor which extend in theX-axis direction. A FinFET-structure transistor and a nanowiretransistor will be described in detail later.

In the following, coupling between the power switch circuit 200 and atarget circuit will be described with reference to FIG. 8. FIG. 8 is adrawing illustrating coupling between a target circuit and the firstpower switch circuit of the first embodiment.

FIG. 8 illustrates an example in which a target circuit 91 and a targetcircuit 92 are implemented on the right-hand side of the well-tap area22-2 of the power switch circuit 200 according to the presentembodiment. The target circuits 91 and 92 are examples of standardcells.

The target circuit 91 is an inverter including an input terminal T1 andan output terminal T2. The target circuit 92 is a NAND gate including aninput terminal T3 and an output terminal T4.

In the example illustrated in FIG. 8, an N-type well 93 of the targetcircuit 91 and the target circuit 92 is connected to the N-type well 204of the well-tap area 22-2, thereby receiving potential applied thereto.

It may be noted that the inverter and the NAND gate are examples ofstandard cells, and standard cells are not limited to these examples.

In the following, the power switch circuit 210, which is the secondpower switch circuit of the present embodiment, will be described withreference to FIG. 9.

FIG. 9 is a drawing illustrating the second power switch circuitaccording to the first embodiment. The power switch circuit 210 of thepresent embodiment differs from the power switch circuit 200 in that thewell-tap areas 22-1 and 22-2 are not provided.

The power switch circuit 210 of the present embodiment includes anN-type well 302 formed in the P-type substrate 201. The power switchcircuit 210 of the present embodiment further includes a power supplyline 305 corresponding to the power supply line VDD, a power supply line306 corresponding to the power supply line VVDD, and power supply lines307 corresponding to the power supply line VSS.

The power supply line 305, which is formed over the P-type substrate201, is electrically coupled to the N-type well 302. The power supplyline 306 is formed over the P-type substrate 201 to span across theN-type well 302 in a plan view.

A transistor 35 is formed to provide coupling between the power supplyline 305 and the power supply line 306 in the N-type well 302. The gateelectrode of the transistor 35 is coupled to the output of the firstinverter 37 of a buffer 36. The transistor 35 of the present embodimentmay include the same structure as the transistor 25. The buffer 36 mayinclude the same structure as the buffer 26. The term “same structure”refers to the sameness of a circuit or a transistor formed based on thesame design layout, allowing for differences resulting from productvariation in the size and shape of each structural element constitutingthe transistors 25 and 35 and the buffers 26 and 36.

In the following, the power switch circuit 210 of the present embodimentwill be described with reference to FIG. 10 and FIG. 11.

FIG. 10 is a drawing illustrating the layout of the second power switchcircuit according to the first embodiment. FIG. 11 is a drawingillustrating a cross-section of the second power switch circuitaccording to the first embodiment. FIG. 11 illustrates the cross sectiontaken along the X-X′ line in FIG. 10.

The power switch circuit 210 of the present embodiment includes a powerswitch section and end-cap areas 32-1 and 32-2 formed on the respectivesides of the power switch section 31. The end-cap areas 32-1 and 32-2are the areas in which dummy transistor structures are formed.

In the present embodiment, provision of the end-cap areas 32-1 and 32-2serves to ensure the homogeneity of transistor production processes,thereby stabilizing the characteristics of transistors.

The power switch circuit 210 of the present embodiment includes theN-type well 302, the power supply lines 305 through 307, gate electrodes308, P-type impurity regions 321 through 324, N-type impurity regions331 through 336, and contacts 312 and 316 through 318.

The power switch circuit 210 of the present embodiment includes theN-type well 302 formed in the P-type substrate 201. The P-type impurityregions 321 through 324 and the N-type impurity region 331 are formed inthe N-type well 302. In the present embodiment, the N-type impurityregion 332 through 336 are formed in the P-type substrate 201.

The P-type impurity regions 321, which have a higher dopingconcentration than the P-type substrate 201, form the source and drainregions of the transistor 35. The transistor 35 includes the gateelectrodes 308, gate insulating films 352, and sidewalls 353 and 354. Inthe present embodiment, the gate electrodes 308 are electrically coupledto the output of the inverter 37. In the present embodiment, a pluralityof transistors 35 may be coupled in parallel to each other.

The transistors of inverters of the buffer 36 include source and drainregions as a part of the P-type impurity regions 322 and the N-typeimpurity regions 332. The P-type impurity regions 322 have a higherdoping concentration than the P-type substrate 201. The transistors ofthe inverters constituting the buffer 36 include gate electrodes 371,gate insulating films 372, and sidewalls 373 and 374.

The end-cap area 32-1 includes a P-type impurity region 323 and N-typeimpurity regions 333 and 334, which are coupled to none of the powersupply lines 305, 306, and 307. The end-cap area 32-2 includes a P-typeimpurity region 324 and N-type impurity regions 335 and 336, which arecoupled to none of the power supply lines 305, 306, and 307.

The end-cap areas 32-1 and 32-2 adjoin the power switch section 31 onthe respective sides thereof.

The power switch circuit 210 of the present embodiment includes the STIs381 through 383 formed in the P-type substrate 201 between thetransistors. Further, a first interlayer insulating film 261 is formedover the P-type substrate 201.

Some of the P-type impurity regions 321 are coupled to the power supplyline 305 through the contacts 312 formed through the first interlayerinsulating film 261, and the others are coupled to the power supply line306 through the contacts 316 formed through the first interlayerinsulating film 261.

One of the P-type impurity regions 322 is coupled to the power supplyline 305 through the contact 318 formed through the first interlayerinsulating film 261.

The P-type impurity regions 321 and the P-type impurity regions 322 areisolated from each other by the STI 382. The P-type impurity regions 321and the N-type impurity region 331 are isolated from each other by theSTI 383. The N-type impurity region 331 is coupled to the power supplyline 305 through the contact 317 formed through the first interlayerinsulating film 261, thereby coupling the N-type well 302 to the powersupply line 305.

As described above, the power switch circuit 210 of the presentembodiment does not include well-tap areas, thereby having a width inthe X direction that is narrower than that of the power switch circuit200. Placing the power switch circuits 210 in the second area 43 thusserves to reduce the entire circuit size, compared with the case inwhich the power switch circuits 200 are placed in the second area 43.

In the present embodiment, the dummy transistor structures in theend-cap areas 32-1 and 32-2 do not need to receive the potential of thepower supply line VVDD. Unlike the power switch circuit 200, thus, thepower switch circuit 210 does not include N-type wells receiving thepotential of the power supply line VVDD which needs to be electricallyisolated from the N-type well 302. This allows the end-cap areas 32-1and 32-2 to be disposed near the power switch section 31, which allowsthe power switch circuit 210 to be made smaller than the power switchcircuit 200.

In the present embodiment, the P-type impurity region 323 and the P-typeimpurity region 324 are both disposed inside the N-type well 302.Alternatively, the P-type impurity region 323 and the P-type impurityregion 324 may be formed outside the N-type well 302, i.e., in theP-type substrate 201.

The power switch circuit 210 of the present embodiment includes theend-cap areas 32-1 and 32-2. Alternatively, the end-cap areas 32-1 and32-2 may not be provided. With reference to FIG. 12, a power switchcircuit 210A including no end-cap areas 32-1 and 32-2 will be described.

FIG. 12 is a drawing illustrating another layout of the second powerswitch circuit according to the first embodiment.

The power switch circuit 210A illustrated in FIG. 12 differs from thepower switch circuit 210 only in that the end-cap areas 32-1 and 32-2are not provided.

The absence of the end-cap areas 32-1 and 32-2 allows the size of thepower switch circuit 210A illustrated in FIG. 12 to be further reducedthan the power switch circuit 210 by a corresponding amount.

The contacts 312 and 316 through 318 of the present embodiment include aglue film which includes titanium nitride, and a tungsten film, forexample. The power supply lines 305 through 307 include copper and abarrier metal film which includes tantalum or tantalum nitride, forexample. The STIs 381 through 383 may include a silicon dioxide film,for example. In the present embodiment, the gate electrodes 308 and 371may include polysilicon or metal such as titanium nitride. The gateinsulating films 352 and 372 may include a silicon dioxide film or afilm which includes one or more materials of an oxide of hafnium,zirconium, lanthanum, yttrium, aluminum, titanium, and tantalum.

In the following, the power supply lines of the semiconductor device 30of the present embodiment will be described with reference to FIG. 13.FIG. 13 is a drawing illustrating the power supply lines of thesemiconductor device according to the first embodiment. FIG. 13illustrates an enlarged view of the second area 43 and the vicinitythereof in the semiconductor device 30 illustrated in FIG. 3.

The semiconductor device 30 includes power supply lines 131, 132, and133. The power supply lines 131 serve to supply potential to the powersupply lines VDD of the power switch circuits 200 and the power switchcircuits 210. The power supply lines 132 serve to supply potential tothe power supply lines VSS of the power switch circuits 200 and thepower switch circuits 210. The power supply lines 133 serve to supplypotential to the power supply lines VVDD of the power switch circuits200 and the power switch circuits 210.

The semiconductor device 30 illustrated in FIG. 13 includes the standardcells 40 disposed in the first area 42 The power supply lines 131, 132,and 133 extend in the Y-axis direction for coupling to the power switchcircuits 200 and to the power switch circuits 210.

The power supply lines 131 may be electrically coupled to each other.The power supply lines 132 may be electrically coupled to each other.The power supply lines 133 may be electrically coupled to each other.Specifically, an interconnection coupled to the power supply lines 131,an interconnection coupled to the power supply lines 132, and aninterconnection coupled to the power supply lines 133 may be formed inanother interconnection layer different from the interconnection layerin which power supply lines 131, 132, and 133 are formed (not shown).

Although the power supply lines 131, 132, and 133 in FIG. 13 arearranged in such a manner as to overlap the power switch circuits 200 orthe power switch circuits 210 in a plan view, this is not a limitingexample. In the present embodiment, only the power supply lines 131 maybe disposed such as to overlap the power switch circuits 200 or thepower switch circuits 210 in a plan view, while the power supply lines132 and 133 may be disposed at any locations in the first area 42 or thesecond area 43. Although the configuration illustrated in FIG. 13includes the power supply lines 131, 132, and 133, this is not alimiting example. The semiconductor device 30 illustrated in FIG. 13includes the power supply lines 132 and 133 for the purpose of couplingthe contact points of the power supply lines VSS to each other andcoupling the contact points of the power supply lines VVDD to eachother. When there is no need for such coupling, only the power supplylines 131 may be provided.

According to the present embodiment described above, power switchcircuits usable for respective, different types of target circuits areprovided.

Specifically, the present embodiment provides the power switch circuits200 for target circuits including no areas for applying potential to thesubstrate, and also provides the power switch circuits 210 for targetcircuits including areas for applying potential to the substrate. Sincethe power switch circuit 210 does not include the well-tap areas 22-1and 22-2, the power switch circuit 210 has a smaller size than the powerswitch circuit 200. The present embodiment thus serves to reduce thesize of the semiconductor device 30.

The circuits 50 and the standard cells 40 in the present embodiment mayreceive the potential of the power supply line VVDD based on the samepower supply line VDD. Specifically, the power supply line 205 and thepower supply line 305 may be coupled to each other, and the power supplyline 206 and the power supply line 306 may be coupled to each other.Further, the power supply line 207 and the power supply line 307 may becoupled to each other.

The circuits 50 and the standard cells 40 may alternatively receive thepotential of the power supply line VVDD based on different power supplylines VDD.

Second Embodiment

In the following, a second embodiment will be described with referenceto the accompanying drawings. The second embodiment differs from thefirst embodiment in that the power switch section includes twobuffer-and-transistor stages, and includes two inputs and two outputs.In the description of the second embodiment in the following,differences from the first embodiment are only described. The same orsimilar elements as those of the first embodiment are referred to by thesame or similar reference symbols, and a description thereof will beomitted.

FIG. 14 is a drawing schematically illustrating a power switch circuitaccording to the second embodiment. FIG. 14 illustrates a power switchcircuit 200A as an example.

The power switch circuit 200A of the present embodiment includestransistors 25 and 45, buffers 26 and 46, a T_(IN)1 terminal, a T_(OUT)1terminal, a T_(IN)2 terminal, a T_(OUT)2 terminal, a T_(VDD) terminal, aT_(VVDD) terminal, and a T_(VSS) terminal.

The T_(IN)1 terminal, which is coupled to the input of the buffer 26,receives a control signal for controlling whether to supply or cut thepower to a target circuit. The T_(OUT)1 terminal is coupled to theoutput of the buffer 26.

The transistor 45 of the present embodiment is a switch transistor. Thebuffer 46, which includes an inverter 47 and an inverter 48, drives thetransistor 45.

The T_(IN)2 terminal, which is coupled to the input of the buffer 46,receives a control signal for controlling whether to supply or cut thepower to a target circuit. The T_(OUT)2 terminal, which is coupled tothe output of the buffer 46, transmits the control signal applied to theT_(IN)2 terminal. The T_(VDD) terminal, which is coupled to one end ofthe transistor 45, is coupled to the power supply. The T_(VVDD)terminal, which is coupled to the other end of the transistor 45, iscoupled to the target circuit.

The transistor 45 is a PMOS transistor having the on and off stateswhich are controlled in response to the signal supplied from theinverter 47 of the buffer 46. The inverter 47 is coupled between thepower supply line VSS and the power supply line VDD via the T_(VSS)terminal and the T_(VDD) terminal, respectively. The T_(VSS) terminal isa ground connection terminal that is coupled to the ground.

In the present embodiment, the on state of the transistor 25 or 45causes the T_(VDD) terminal and the T_(VVDD) terminal to be coupled toeach other, so that the power supply potential to which the T_(VDD)terminal is connected is supplied to the T_(VVDD) terminal. The powersupply potential is thus supplied from the T_(VVDD) terminal to thetarget circuit. In the case of the transistors 25 and 45 being both inthe on state, the power supply potential with a larger amount of currentthan in the case of only one of these being in the on state is suppliedto the target circuit.

In the following, coupling between the well-tap areas 22-1 and 22-2 andthe power supply to the power switch circuit 200A of the presentembodiment will be described with reference to FIG. 15. FIG. 15 is adrawing illustrating coupling between the well-tap areas and powersupply of a first power switch circuit of the second embodiment.

A power switch circuit 200A of the present embodiment includes a powerswitch section 21A and well-tap areas 22-1 and 22-2.

The power switch section 21A includes the transistor 45 connectedbetween the power supply line 205 corresponding to the power supply lineVDD and the power supply line 206 corresponding to the power supply lineVVDD, with the gate electrode of the transistor 45 being coupled to theinverter 47 at the first stage of the buffer 46. The buffer 46 iscoupled between the power supply line 205 and the power supply lines207.

In the following, a power switch circuit 210B of the present embodimentwill be described with reference to FIG. 16. FIG. 16 is a drawingillustrating the second power switch circuit according to the secondembodiment.

The power switch circuit 210B of the present embodiment includes theN-type well 302 formed in the P-type substrate 201. The power switchcircuit 210B of the present embodiment further includes a power supplyline 305 corresponding to the power supply line VDD, a power supply line306 corresponding to the power supply line VVDD, and power supply lines307 corresponding to the power supply line VSS.

A transistor 55 is formed to provide coupling between the power supplyline 305 and the power supply line 306 in the N-type well 302. The gateelectrode of the transistor 55 is coupled to the output of the firstinverter 57 of the buffer 56. The transistor 55 of the presentembodiment may include the same or similar structure as the transistor35.

The inverter 57 and the inverter 58 are coupled between the power supplyline 305 and the power supply lines 307.

As described above, the power switch circuit 200A and the power switchcircuit 210B of the present embodiment include the power switch sections21A and 31A, respectively, each of which includes 2 inputs and 2outputs. The configuration of the power switch section 21 is not limitedto the configuration used in the first or second embodiment. The powerswitch section may have any configuration as long as a transistorserving as a switch to control whether to supply or cut the powervoltage is provided.

Third Embodiment

In the following, a third embodiment will be described with reference tothe accompanying drawings. The third embodiment differs from the firstembodiment in that there is an increased number of contact pointsbetween the power supply lines 205 and 206 and the P-type impurityregions 221 serving as the source and drain regions of the transistor25. In the description of the third embodiment in the following,differences from the first embodiment are only described. The same orsimilar elements as those of the first embodiment are referred to by thesame or similar reference symbols, and a description thereof will beomitted.

FIG. 17 is a drawing illustrating the layout of the first power switchcircuit according to the third embodiment. In the power switch circuit200B of the present embodiment, the power supply lines 205 and 206bifurcate as shown in an area 171 over the P-type impurity regions 221formed in the N-type well 202 of the power switch section 21B.

In the present embodiment, a power supply line 205B coupled to the powersupply line VDD is formed in an area 172 over the P-type impurityregions 221 of the power switch section 21B.

A power supply line 205A branching off of the power supply line 205 anda power supply line 206A branching off of the power supply line 206extend in the area 171.

The power supply line 205A is coupled through contacts 173 to the P-typeimpurity regions 221. The power supply line 206A is coupled throughcontacts 174 to the P-type impurity regions 221. The power supply line205B is coupled through contacts 175 to the P-type impurity regions 221.

Namely, the P-type impurity regions 221 are coupled to the power supplylines 205, 205A, and 205B, so that there is an increased number ofcontact points for coupling to the power supply line VDD compared withthe first and second embodiments. The present embodiment thus enablesthe reduction of resistance along the power supply lines.

Although the power switch circuit 200B was described in connection withFIG. 17, the power supply line 305 and the power supply line 306 maysimilarly bifurcate in the case of the power switch circuit 210, therebyincreasing the number of contact points between the power supply linesand the P-type impurity regions 321 of the transistor 35.

In the following, a FinFET and a nanowire transistor will be describedwith reference to FIG. 18 and FIG. 19.

FIG. 18 is a drawing schematically illustrating a FinFET. A FinFET 181illustrated in FIG. 18 includes a three-dimensional structure referredto as a fin 403 serving as a source 401 and a drain 402, unlike a MOStransistor having a two-dimensional structure. The FinFET 181 furtherincludes a gate 404 surrounding the fin 403.

The structure of the FinFET 181 including the fin 403 provides threesurfaces of the fin 403 defining the channel region, thereby improvingthe controllability of a channel.

FIG. 19 is a drawing schematically illustrating a nanowire transistor. Atransistor 191 illustrated in FIG. 19 includes a source region 503 and adrain region 504 projecting from an STI 502 formed in an Si substrate501.

The source region 503 and the drain region 504 of the transistor 191 arecoupled to each other through nanowires 506. Gate insulating films 507are formed to surround the nanowires 506, and a gate electrode 505 isformed to cover the gate insulating films 507. Electric current flowsthrough the nanowires 506 when the transistor 191 is in the on state.

The FinFETs illustrated in FIG. 18 or nanowire transistors illustratedin FIG. 19 may be used as the first through third transistors 25, 35,45, and 55.

Although the invention has been described by referring to embodiments,the invention is not limited to the configurations of these embodiments.Various variations and modifications may be made without departing fromthe scope of the present invention, and may be made in accordance withapplications.

What is claimed is:
 1. A semiconductor device, comprising: a firstcircuit formed in a semiconductor substrate; a second circuit formed inthe semiconductor substrate; a first power supply line; a second powersupply line coupled to the first circuit; a first ground line; a thirdpower supply line; a fourth power supply line coupled to the secondcircuit; a second ground line; a first switch circuit including a firstswitch transistor and a well tap of the semiconductor substrate, thefirst switch transistor including a first source and a first drain, oneof the first source and the first drain being coupled to the first powersupply line, another of the first source and the first drain beingcoupled to the second power supply line, and the well tap beingelectrically coupled to the second power supply line; and a secondswitch circuit including a second switch transistor, the second switchtransistor including a second source and a second drain, one of thesecond source and the second drain being coupled to the third powersupply line, another of the second source and the second drain beingcoupled to the fourth power supply line, the second switch circuitincluding no well tap of the semiconductor substrate electricallycoupled to the fourth power supply line.
 2. The semiconductor device asclaimed in claim 1, wherein the second power supply line, the fourthpower supply line, the first ground line, and the second ground lineextend in a first direction, and a length of the second switch circuitin the first direction is shorter than a length of the first switchcircuit in the first direction.
 3. The semiconductor device as claimedin claim 2, wherein the first switch circuit is located alongside thefirst circuit, and the second switch circuit is located alongside thesecond circuit.
 4. The semiconductor device as claimed in claim 2,wherein the semiconductor device includes a plurality of the secondswitch circuits, the plurality of the second switch circuits arearranged alongside the second circuit, and the second switch circuitsare aligned in a second direction perpendicular to the first direction.5. The semiconductor device as claimed in claim 2, wherein thesemiconductor device includes a plurality of the second circuits, andthe second switch circuit is located between two of the second circuitsin a plan view.
 6. The semiconductor device as claimed in claim 2,wherein the fourth power supply line and the second ground line areterminated at an edge of a design area which includes the first circuitand the second circuit, and the second switch circuit is located betweenthe edge of the design area and the second circuit.
 7. The semiconductordevice as claimed in claim 2, wherein the second switch circuit includeend-cap areas arranged alongside the second switch transistor onrespective sides of the second switch transistor in the first direction.8. The semiconductor device as claimed in claim 2, wherein a secondcircuit includes a terminal electrically coupled to the first circuit,the terminal is located at a first side of the second circuit, and thesecond switch circuit is located alongside a second side of the secondcircuit which is opposite to the first side.
 9. The semiconductor deviceas claimed in claim 2, wherein the first power supply line bifurcates inthe first switch circuit in a plan view, the second power supply linebifurcates in the first switch circuit in a plan view, the first powersupply line is coupled to one of the first source and the first drain ofthe first switch transistor via a plurality of first contacts which areformed on the semiconductor substrate, the second power supply line iscoupled to another of the first source and the first drain of the firstswitch transistor via a plurality of second contacts which are formed onthe semiconductor substrate, the third power supply line bifurcates inthe second switch circuit in a plan view, the fourth power supply linebifurcates in the second switch circuit in a plan view, the third powersupply line is coupled to one of the second source and the second drainof the second switch transistor via a plurality of third contacts whichare formed on the semiconductor substrate, and the fourth power supplyline is coupled to another of the second source and the second drain ofthe second switch transistor via a plurality of fourth contacts whichare formed on the semiconductor substrate.
 10. The semiconductor deviceas claimed in claim 1, wherein the first switch transistor and thesecond switch transistor have the same structure.